From mboxrd@z Thu Jan 1 00:00:00 1970 Reply-To: kernel-hardening@lists.openwall.com Sender: Vasiliy Kulikov Date: Thu, 23 Jun 2011 19:21:37 +0400 From: Vasiliy Kulikov Message-ID: <20110623152137.GA2536@albatros> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline Subject: [kernel-hardening] [PATCH v2] kernel: escape non-ASCII and control characters in printk() To: Andrew Morton , James Morris , Ingo Molnar , Namhyung Kim , Greg Kroah-Hartman , kernel-hardening@lists.openwall.com, linux-kernel@vger.kernel.org, Alan Cox List-ID: This patch escapes control characters fed to printk() except '\n' and '\t'. There are numerous printk() instances with user supplied input as "%s" data, and unprivileged user may craft log messages with substrings containing control characters via these printk()s. Control characters might fool root viewing the logs via tty, e.g. using ^[1A to suppress the previous log line. On the testing Samsung Q310 laptop there are no users of chars outside of the restricted charset. v2 - Allow chars with code >127. Allow tabs. Reported-by: Solar Designer Signed-off-by: Vasiliy Kulikov --- kernel/printk.c | 17 ++++++++++++++++- 1 files changed, 16 insertions(+), 1 deletions(-) --- diff --git a/kernel/printk.c b/kernel/printk.c index 3518539..727ff7d 100644 --- a/kernel/printk.c +++ b/kernel/printk.c @@ -41,6 +41,7 @@ #include #include #include +#include #include @@ -671,6 +672,20 @@ static void emit_log_char(char c) logged_chars++; } +static void emit_log_char_escaped(char c) +{ + char buffer[8]; + int i, len; + + if (!iscntrl(c) || (c == '\n') || (c == '\t')) + emit_log_char(c); + else { + len = sprintf(buffer, "#x%02x", c); + for (i = 0; i < len; i++) + emit_log_char(buffer[i]); + } +} + /* * Zap console related locks when oopsing. Only zap at most once * every 10 seconds, to leave time for slow consoles to print a @@ -938,7 +953,7 @@ asmlinkage int vprintk(const char *fmt, va_list args) break; } - emit_log_char(*p); + emit_log_char_escaped(*p); if (*p == '\n') new_text_line = 1; } ---